Pneumatic tire with improved crown durability

ABSTRACT

The invention is directed to pneumatic tires for heavy vehicle service that include a carcass, a tread disposed radially outward of the carcass, a sidewall intersecting the tread at a shoulder, and a belt reinforcing structure positioned radially between the carcass and the tread. The belt reinforcing structure includes four belt layers, each layer reinforced by parallel cords the four belts characterized by their cord orientation and angles. A first radially inner belt layer, an adjacent second belt layer overlaying the first belt layer and a third belt layer overlaying the second belt layer are all oriented directionally extending right (R) relative to an equatorial center plane of the tire, a fourth radially outer belt layer overlaying the third belt layer has cords directionally extending left (L). The pneumatic tires of the invention containing these belt layers have improved crown durability and stiffness while maintaining the same overall tire weight.

RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 13/219,829filed on Aug. 29, 2011 entitled “Pneumatic Tire With Improved CrownDurability”.

TECHNICAL FIELD

The present invention generally relates to pneumatic tires and, morespecifically, to pneumatic tires for use on large commercial vehicles.

BACKGROUND OF THE INVENTION

Pneumatic tires for severe service applications on heavy vehicles thatoperate at slow speeds, such as refuse trucks, construction trucks,buses and tankers, are prone to significant heat buildup in the tirecrown area. The heat buildup reduces both belt edge durability and crowndurability. Conventional pneumatic tires incorporate a belt package thatincludes multiple cut belt layers wrapped about the circumference of thetire. Typically, the cut belt layers in conventional pneumatic tires foruse on such heavy vehicles are formed from a single type of belt wireand are narrower in width than the tire footprint. Conventionally, thewidth of the widest cut belt layer is less than 90% of the tirefootprint. The belt layers are most typically stacked in layers with thecords being oriented equally, but oppositely directed between adjacentlayers.

One specific type of pneumatic tire, the 11R24.5 G286 LR ‘H’ tire, foruse in severe service applications is constructed with four individualcut belts each formed from a single type of belt wire. Two of the cutbelt layers are deemed the working belt layers. The green widths of theworking belt layers of the LR ‘H’ tire, which has a footprint width of7.89″, are 7.00″ and 7.80″, respectively, and the corresponding curedbelt widths are 6.40″ and 7.00″, respectively. The cured belt widths areapproximately 81% and 89% of the tire footprint, respectively. Thecontribution of the two working belts alone to the overall tire weightis 14.31 lbs. Individually, the weight contribution for one working beltis about 6.79 pounds and the weight contribution for the other workingbelt, which is the wider of the two working belts, is about 7.52 pounds.

To solve this durability issue, the inventor John Kotanides Jr. in U.S.Pat. No. 7,267,149 proposed a pneumatic tire for service on heavyvehicles having a belt package with widened belts. The tire included abelt reinforcing structure or belt package having multiple cut belts ofwhich one of the cut belts has a width approximately equal to the tirefootprint. Widening two of the cut belts and forming at least one of thewidened cut belts from a lighter material serves to improve tiredurability in the regions of the tire crown and shoulder withoutincreasing the overall tire weight.

In service applications like commercial bus tires, not only is the crownregion subject to high temperatures, but also the bead area adjacent thehot brakes become overheated during use.

Tires under exposure to heavy loads and constant stops for braking suchas buses and waste haulers see extremely high service temperatures.These high temperatures reduce the life of the tires. One way to reducetire heat buildup is to cut the weight of some of the belt layers as thewidth was increased as was accomplished in U.S. Pat. No. 7,267,149. Thisis only feasible if the tire is made sufficiently strong for itsrequired service application. A cool running, but inferior strength tirecasing is not a workable solution. It is this dilemma that is mostdifficult and challenging to solve when designing tires for these heavyloaded commercial vehicles such as waste haulers and buses.

For these and other reasons, it would be desirable to modify pneumatictires for severe service applications on heavy vehicles so as to improvetire durability and stiffness without significantly increasing tireweight.

SUMMARY OF THE INVENTION

The invention is directed to pneumatic tires for heavy vehicle servicethat include a carcass, a tread disposed radially outward of thecarcass, a sidewall intersecting the tread at a shoulder, and a beltreinforcing structure positioned radially between the carcass and thetread. The belt reinforcing structure includes four belt layers, eachlayer reinforced by parallel cords the four belts characterized by theircord orientation and angles. A first radially inner belt layer, anadjacent second belt layer overlaying the first belt layer and a thirdbelt layer overlaying the second belt layer are all orienteddirectionally extending right (R) relative to an equatorial center planeof the tire, a fourth radially outer belt layer overlaying the thirdbelt layer has cords directionally extending left (L). The pneumatictires of the invention containing these belt layers have improved crowndurability and stiffness while maintaining the same overall tire weight.

DEFINITIONS

As used herein and in the claims.

“Axial” and “axially” means the lines or directions that are parallel tothe axis of rotation of the tire.

“Bead” means that part of the tire comprising an annular tensile memberwrapped by ply cords and shaped, with or without other reinforcementelements such as flippers, chippers, apexes, toe guards and chafers, tofit the design rim.

“Carcass” means the tire structure apart from the belt structure, tread,undertread, and sidewall rubber over the plies, but including the beads.

“Cord” means one of the reinforcement strands of which the plies in thetire are comprised.

“Crown” refers to substantially the outer circumference of a tire wherethe tread is disposed.

“Circumferential” means circular lines or directions extending along thesurface of the sidewall perpendicular to the axial direction.

“Cut belt or cut breaker reinforcing structure” means at least two cutlayers of plies of parallel cords, woven or unwoven, underlying thetread, unanchored to the bead, and having both left and right cordangles in the range from 10 degrees to 33 degrees with respect to theequatorial plane of the tire.

“Equatorial plane (EP)” means the plane perpendicular to the tire's axisof rotation and passing through the center of its tread.

“Footprint” means the contact patch or area of contact of the tire treadwith a flat surface at zero speed and under normal load and pressure.

“Inner” means toward the inside of the tire.

“Lateral” means a direction parallel to the axial direction, as inacross the width of the tread or crown region.

“Outer” means toward the tire's exterior.

“Pneumatic tire” means a laminated mechanical device of generallytoroidal shape, usually an open-torus having beads and a tread and madeof rubber, chemicals, fabric and steel or other materials.

“Radial” and “radially” mean directions radially toward or away from theaxis of rotation of the tire.

“Shoulder” means the upper portion of sidewall just below the treadedge.

“Sidewall” means that portion of a tire between the tread and the beadarea.

“Tread” means a molded rubber component which, when bonded to a tirecasing, includes that portion of the tire that comes into contact withthe road when the tire is normally inflated and under normal load.

BRIEF DESCRIPTION OF THE DRAWINGS

The structure The accompanying drawing, which is incorporated in andconstitutes a part of this specification, illustrates an embodiment ofthe invention and, together with a general description of the inventiongiven above, and the detailed description given below, serves to explainthe invention.

FIG. 1 is a cross-sectional view of a pneumatic tire in accordance withan embodiment of the invention.

FIG. 2 is a plan view showing the four belt layers of the belt structureof the tire of FIG. 1 and the direction and orientation of the cord ineach belt layer.

FIG. 3 is an enlarged cross section of a shoulder portion of the tire ofFIG. 1 showing the belt edges.

FIG. 4 is a plan view similar to FIG. 2, but depicting an alternateembodiment tire belt structure made as a mirror image of the beltstructure in FIG. 2.

FIG. 5 is an exemplary cross section of any one of the belt layers.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the FIGS. 1 and 3, a pneumatic tire 10 includes acarcass 12, a ground-engaging tread 14, a sidewall 16, and a shoulder 18defined at the juncture between the sidewall 16 and the tread 14. Thetread 14 has a ground contacting surface 27 separated by grooves 29.When mounted on a vehicle, the tread 14 furnishes traction and tire 10contains a fluid that supports the vehicle load. The tire carcass 12 hasone or more carcass plies 7 extending from the bead 15 under the beltstructure 20 to the opposite bead 15. Radially inward of the at leastone ply 7 is an air impervious inner liner 8. Pneumatic tire 10 isunderstood to have mirror symmetry for reflection about an equatorialplane EP bisecting tire 10 so that the following description isunderstood to apply to the full tire width. Pneumatic tire 10 has afootprint (FP), as described hereinabove.

Arranged radially between the carcass 12 and the tread 14 is a beltpackage 20, generally indicated by reference numeral 20, that includes aplurality of, for example, four individual cut belt plies or layers 22,24, 26, and 28. The cut belt layers 22, 24, 26, and 28 are formed ofpolyester, nylon or aramid cord or monofilament steel cord reinforcementencased inside a corresponding elastomer coating. The cut belt layers22, 24, 26, and 28 reinforce a crown 30 of the tire 10 and are appliedto the tire 10 as individual spliced sheets of cord reinforcement. Atread cushion 32 is provided radially outward of the cut belt layers 22,24, 26, and 28 for joining the tread 14 with the belt package 20. In thetire making process, the green carcass 12, tread 14, sidewalls 16 andbelt package 20 are united and then mounted in a curing mold forvulcanizing the tire 10.

In a preferred embodiment of the invention, the pneumatic tire 10 has abelt reinforcing structure 20 positioned between the carcass 12 and thetread 14. The belt reinforcing structure 20 includes four belt layers, aradially inner first belt layer 22, a second belt layer 24 arrangedadjacent to and radially outward from the first belt layer 22 and athird belt layer 26 overlaying and adjacent to the second belt layer 24and a fourth belt layer 28 overlaying and radially outward of the thirdbelt layer 26. As shown in FIG. 5, each belt layer 22, 24, 26, 28 isreinforced with a plurality of parallel cords 32. As shown in FIG. 2,the four layer belt structure 20 is characterized by having the first22, second 24 and third 26 belt layers having cords directionallyoriented relative to an equatorial center plane EP of the tire 10extending to the right (R) whereas the fourth belt layer 28 has thecords extending to the left (L) to form a four layer stacked beltstructure 20 of cords sequentially oriented RRRL. In the preferredembodiment, the first belt layer 22 and second belt layer 24 have theparallel cords oriented right (R) angularly in a range of 45 to 65degrees relative to the equatorial plane. The third belt layer 26 hasthe cords oriented right (R) in a range of 16 to 25 degrees relative tothe equatorial plane. The fourth belt layer 28 is oriented left (L) in arange 16 to 25 degrees relative to the equatorial plane 19. Preferablythe first belt layer 22 has cords angled at a larger angle than thecords of the second belt layer 24. The cords of the first belt layer 22preferably are 5 degrees right greater than the cords of the second beltlayer 24. In the preferred embodiment, the first belt layer 22 cords areoriented at 50 degrees right (R) and the cords of the second belt layer24 are oriented at 45 degrees right (R). The cords of the fourth beltlayer 28 are oriented left (L) at an angle greater than the cords of thethird belt layer 26 that are oriented to the right (R). The fourth beltlayer 28 has the cords at least 3 degrees greater than the right (R)cord angles of the third belt layer 26. The third belt layer 26 hascords oriented right (R) at an angle of 19 degrees whereas theoverlaying cords of the fourth belt layer 28 are angled at 23 degreesleft (L).

When this preferred embodiment tire was made in a size 315/80/22.5radial pneumatic tire having the belt structure 20 as described above itwas determined that the second belt layer 24 operated much cooler than aprior art tire. This is believed to be caused by the combination of aRRRL belt structure wherein the underlying first belt layer 22 and theoverlying third belt layer 26 directionally oriented the same as thesecond belt layer 24 assists the second belt layer 24 particularlyaround the belt edges to maintain the cooler temperature than wouldotherwise be achieved by a conventional opposite orientation of adjacentcords within adjacent belt layers. This ability to achieve coolertemperatures in the belt edge region greatly improves the crowndurability of the overall tire structure. It is important to understandthat this structure as described herein in the size tire used for mixedservice heavy loaded vehicles in mixed service applications such aswaste haulers or buses is quite beneficial in that it assists the beltstructure in maintaining its structural integrity due to the fact thatit operates at a much cooler temperature than heretofore achieved.

In a test trial run a prior art tire having a conventional beltstructure having four belt layers oriented at RRLL had an internal tirecavity temperature of 121.5 degrees C. and an interlaminate shear of0.701. The prior art control tire had the four belt layers oriented fromthe radially inner through the radially outer at 55 degrees R, 18degrees R, 18 degrees L and 18 degrees L respectively. Both the priorart control tire and the tire 10 of the invention had the cords of thefirst inner belt at 10 EPI (ends per inch) and the remaining three beltsat 14 EPI each. The cords 32 in the belts 24, 26 and 28 were UD14 cordswhich is a 3+3×0.35 ST steel wire construction. The radially inner belt22 used cords 32 made of US10 which is a 3+2×0.35 ST steel wireconstruction. The inventive tire of the RRRL belt construction with 50degrees R, 45 degrees R, 19 degrees R and 23 degrees L had a cavitytemperature of 114.5 degrees C. and an interlaminar shear rating of0.285. This was a considerable difference and evidences far betteroperating performance at the belt edges.

It is important to note with reference to FIG. 4 that an alternativetire belt structure can be constructed wherein the RRRL belt layers 22,24, 26, 28 of the preferred invention can be produced as a mirror imagehaving a LLLR belt structure. This mirror image belt structure when madesimilar to that previously described using the same ranges of cordangles only oppositely oriented when assembled is expected to perform aswell as the test tires made with a RRRL configuration. It is importantto note that any mirror image of the construction is considered withinthe scope of the present invention. What is important is that thedirectionally same orientation of the first 22, second 24 and third belt26 layers achieves a great assistance for the second belt layer 24 inthe belt edge region such that the second belt layer 24 will achieve acooler operating temperature than would otherwise be achieved.

While the present invention has been illustrated by a description ofvarious embodiments and while these embodiments have been described inconsiderable detail, it is not the intention of the applicant torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. Thus, the invention in its broader aspects istherefore not limited to the specific details, representative apparatusand method, and illustrative example shown and described. Accordingly,departures may be made from such details without departing from thespirit or scope of applicant's general inventive concept.

What is claimed is:
 1. A pneumatic tire for heavy vehicle service,comprising: a carcass; a tread disposed radially outward of saidcarcass; a sidewall intersecting said tread at a shoulder; a beltreinforcing structure positioned radially between said carcass and saidtread, said belt reinforcing structure being four belt layers, aradially inner first belt layer and a second belt layer arrangedadjacent to and radially outward from said first belt, a third beltlayer overlaying and adjacent to said second belt layer and a fourthbelt layer overlaying and radially outward of said third belt layer,each belt layer being reinforced with a plurality of parallel cords, thebelt structure characterized by having the first, second and third beltlayers having the cords directionally oriented relative to an equatorialcenter plane of the tire extending to the left (L) and the fourth beltlayer having the cords extending to the right (R) to form a four layerstacked belt structure of cords sequentially oriented LLLR; and whereinthe first belt layer and second belt layer have the parallel cordsoriented left (L) angularly in the range of 45 degrees to 65 degreesrelative to the equatorial plane EP, the third belt layer has cordsoriented left (L) in the range of 16 degrees to 25 degrees relative tothe equatorial plane EP, the fourth belt layer is oriented right (R) inthe range of 16 degrees to 25 degrees relative to the equatorial planeEP and wherein the first belt layer has cords angled at a larger anglethan the cords of the second belt layer, the cords of the fourth beltlayer are oriented to the right (R) at an angle greater than the cordsof the third belt layer that are oriented to the left (L) and the cordangle of the first belt layer is 5 degrees left (L) greater than thecords of the second belt layer and the fourth belt layer has cordsoriented right (R) at least 3 degrees or greater than the left (L) angleof cords of the third belt layer.
 2. The pneumatic tire for heavyvehicle service of claim 1 wherein the cords of the first belt layer areoriented 50 degrees left (L) and the cords of the second belt layer areoriented 45 degrees left (L).
 3. The pneumatic tire for heavy vehicleservice of claim 1 wherein the third belt has cords oriented left (L) atan angle of 19 degrees.
 4. The pneumatic tire for heavy vehicle serviceof claim 3 wherein the cords of the fourth belt layer are angled 23degrees right (R).
 5. A pneumatic tire for heavy vehicle service,comprising: a carcass; a tread disposed radially outward of saidcarcass; a sidewall intersecting said tread at a shoulder; and a beltreinforcing structure positioned radially between said carcass and saidtread, said belt reinforcing structure including four belt layers, aradially inner first belt layer and a second belt layer arrangedadjacent to and radially outward from said first belt, a third beltlayer overlaying and adjacent to said second belt layer and a fourthbelt layer overlaying and radially outward of said third belt layer,each belt layer being reinforced with a plurality of parallel cords, thebelt structure characterized by having the first, second and third beltlayers having the cords directionally oriented relative to an equatorialcenter plane of the tire extending to the left (L) and the fourth beltlayer having the cords extending to the right (R) to form a four layerstacked belt structure of cords sequentially oriented LLLR wherein thecords of the first belt layer are oriented 50 degrees left (L) and thecords of the second belt layer are oriented 45 degrees left (L) andwherein the cords of the third belt layer are oriented left (L) at 19degrees and the cords of the fourth belt layer are oriented right (R) at23 degrees.
 6. The pneumatic tire for heavy vehicle service of claim 5wherein the cords of the first belt layer are 10 EPI and the cords ofthe second, third and fourth belt layers are 14 EPI.
 7. The pneumatictire for heavy vehicle service of claim 6 wherein the cords of the firstlayer are a 3+2×0.35 ST steel wire construction.
 8. The pneumatic tirefor heavy vehicle service of claim 7 wherein the cords of the second,third and fourth layer are a 3+3×0.35 ST steel wire construction.
 9. Thepneumatic tire for heavy vehicle service of claim 8 wherein thepneumatic tire is a radial tire.
 10. The pneumatic tire for heavyvehicle service of claim 9 wherein the radial tire is a size315/80/22.5.
 11. The pneumatic tire for heavy vehicle service of claim 1wherein the cords of the first belt layer are 10 EPI and the cords ofthe second, third and fourth belt layers are 14 EPI.